How do I stop this?

I have an ex-workmate who only messages me for advice (bestie, work, family problems & more). This is has been going on for a few years now. I didn't mind before since I did have free time and also wanted to help. However, I can't help but think now, is it worth my time being worried over someone else's problem? If this person messages me again, I don't know how to refuse. My ppl pleasing self can't refuse ppl in need of advices. Help 😭